A camera module commonly used in a mobile device, such as a cell phone, is provided with a voice coil actuator and moves a lens by driving the voice coil actuator to change its position, thereby performing auto-focusing on a particular object.
The voice coil actuator is a motor that is developed based on the fact that a vibration plate of a speaker moves back and forth when a force caused by the Fleming's left hand rule between a voice current flowing through a voice coil of the speaker and a magnetic force produced by a permanent magnet. As compared with a DC motor or a stepping motor which rotates, since the voice coil actuator reciprocates linearly over a short distance, it can be widely used for precise tracking or focusing.
The above-mentioned voice coil actuator includes a large coil (L; inductor) component. However, the inductor (L) component of the voice coil actuator exhibits high resonance response characteristics due to its own resonance frequency and causes residual vibration during operation, so that there are problems in that an auto-focus function of the camera may be affected or a malfunction is caused.
To address the aforesaid problems, KR 10-0968851 B1 provides an input shaping control technique capable of enhancing an auto-focus function of a camera by reducing undesired residual vibration.
However, the aforesaid input shaping control method does not consider damping, which may exist in any type in reality, the effect of reducing residual vibration is limited.